That was just a very simple example how. 
I’d say play and then read the code for a few games.
I generally suggest Creatures Such As We, since it’s short but there’s a variety of character interactions there. Choice of Romance, (you just need to do the first one).
If you’re looking for complexity have a look at Zombie Exodus. I’d strongly suggest against trying to emulate it though.
Zombie Exodus is a hugely complex game in term of the character interactions, moreso than any of the choice of games. Most characters can like or dislike you, and that influences their reactions to you. On top of that some characters may or may not be present, may or may not be alive, may or may not be in a romantic relationship with you. By the time of the epilogues there’s so many things that need to be taken into consideration.